In the art of cooking food, certain foods are deep-fried, that is, they are immersed in hot shortening or oil for periods of time sufficient to suitably cook them.
In restaurants, fast food service outlets, and the like, deep frying of foods is carried out in applicances called "deep fryers". Deep fryers consist of large upwardly opening vessels in which substantial volumes of shortening or oil are deposited. The vessels have suitable gas or electric heating means and related temperature control means to heat and maintain the shortening or oil in the vessels at desired cooking temperatures.
The ordinary commercial deep fryer includes food retaining cooking baskets to effect controlled immersion of food in the heated oil; rack or hangers for the baskets; drip trays; and various other means to facilitate the effective and efficient cooking and handling of food.
Finally, the ordinary commercial deep fryer is provided with a valve controlled drain fitting at the bottom of its receptacle to facilitate draining of the shortening or oil therefrom, as desired and as circumstances require.
Commercial deep fryers of the general character referred to above are provided in several different sizes. The most popular size of deep fryers are designed to hold and operate efficiently with about fifty pounds of shortening or about 41/2 gallons of oil. The cost of such quantities of shortening or oil presently ranges from about $25 to $50. Further, it is anticipated that the cost of such shortening or oil will increase dramatically in the foreseeable future and is likely to be double the noted cost within the next several years.
In most commercial establishments where deep fryers are used, a multiplicity of deep fryers are provided. In small establishments, it is not infrequent that two or three deep fryers are provided. In large establishments, it is not infrequent that eight or more deep fryers are provided.
In the case of small establishments with three deep fryers, the cost of shortening or oil in use at any given time is frequently about $150, while in the case of establishments with eight deep fryers, the cost of shortening or oil is frequently about $400.
In practice, the shortening or oil used in deep fryers, if not properly cared for, is short-lived and may be usable for from two to four days before the quality of the food cooked therein is adversely affected.
As a result of the foregoing, for obvious economic reasons, and to maintain high quality of the cooked foods, it is established and standard practice to subject the shortening or oil in deep fryers to daily filtering procedures in efforts to extend the useful life of the shortening or oil and to maintain the quality of the goods cooked therein at high standards.
During use of cooking shortening or oil in deep fryers, degradation of the shortening or oil commences as soon as it is heated and the first food to be cooked is immersed therein. Degradation of the shortening or oil continues at an accelerated rate as time elapses and the quantity of food cooked therein increases.
The principal causes of degration of the shortening or oil in deep fryers are oxidation caused by heat and the introduction of water (from the food cooked therein) and the introduction or addition of solid residues from the food cooked therein. The solid residues consist of bits and pieces of foodstuff and fatty acids and the like driven from the food during cooking thereof. The solid residues in the shortening or oil become scorched and result in tainting the shortening or oil and the food which is subsequently cooked therein with undesirable tastes and odors. The scorched residues also result in undesired discoloration of the oil and of the foods which are cooked therein. The fatty acids in the residues in the shortening or oil, in addition to scorching and the adverse effects thereof, react in the shortening or oil to cause and greatly accelerate oxidation and/or general breaking down and degradation thereof.
It has been found that by daily filtering of the shortening or oil used in deep fryers, to remove the collectible solid bits and pieces of food and the fatty acids carried thereby, the useful life of the shortening or oil can be extended from two to three days to from three to eight days. That is, by filtering out readily collectible solids, the life of the shortening or oil can be doubled and the cost thereof, to the operator, can be cut in half.
To the above end, and as noted above, it is a common and necessary practice in properly managed and operated facilities to filter the shortening or oil in deep fryers every day.
It has also been determined and it is well established that if the shortening or oil used in deep fryers can be filtered so as to remove micron and submicron size solids and can be treated to neutralize the fatty acids held in suspension therein, the life of the shortening or oil can be effectively doubled again, that is, its effective and useful life can be extended from six to fifteen days. When the shortening or oil is treated in the foregoing manner, it is said to have been "purified".
As a result of the foregoing, in the commercial food industry, there has developed two common practices for the care and handling of deep fryer shortening or oil.
One practice or procedure is where the operators of deep fryers contract with rendering companies or the like to be continually supplied with fresh shortening or oil to meet their daily needs. In furtherance of such practices or procedures, the rendering companies, on a regular basis, deliver fresh supplies of oil to the operators and pick up the spent or used shortening or oil. The rendering companies filter and purify the used oil which they collect for redistribution and use as fresh material (to the operators they serve).
The other common practice is where the operators of the deep fryers obtain and equip themselves with filtering means or apparatus capable of filtering their shortening or oil to an extent that the useful life thereof is doubled.
This second noted practice is finding ever increasing favor in the commercial food industry since the economic savings attained thereby are comparable with the savings attainable through the services afforded by rendering companies and the like and the operators are more self-sufficient or non-dependent upon outside services.
The ordinary shortening or oil filtering apparatus provided by the prior art, for use by operators of deep fryers, consist of receiver tanks into which the shortening or oil from deep fryers is delivered, under pressure, by means of electric pumps. The tanks are provided with perforated partitions or the like to support paper filter elements or sheets through which the shortening or oil is urged or advanced by the pumps and on which solid particulate matter, of sufficient size to be stopped by the filter paper, collect. The effective filtering surface area of the above noted filtering apparatus provided by the prior art is quite limited and is necessarily such that the screen size of the filter paper used must be sufficiently large so as to permit the passage of micron and sub-micron particles and to thereby prevent premature impacting and plugging up of the filter papers.
It has been found that when the filter papers in the prior art filtering apparatus become plugged and impacted with impurities and the apparatus continue to operate, the paper filters rupture and the entire filtering operations are rendered ineffective.
In the process of purifying shortening and oil, as practiced by commercial rendering companies and the like, the shortening or oil is generally passed through filter beds of fine powdered materials composed of diatomaceous silicia and calcium and/or magnesium silicates. The equipment which is required to effect passing the shortening or oil through such filter beds is so complicated, large and costly that the ordinary operator of deep fryers cannot afford such equipment and his facilities could not accommodate or house such equipment.
In certain of the filtering apparatus provided by the prior art and which use paper filter elements, attempts have been made to add fine powdered filtering material such as referred to above to the shortening or oil with the plan that that material will collect on the paper and establish an effective filter bed. While the foregoing appears sound in principle, it has proven to be unsound and totally impractical since the powdered filtering materials rapidly collects on, compacts and plugs up the limited surface area afforded by the paper filters and stops the filtering operation and/or results in the paper filter elements rupturing and rendering the entire filtering and/or purifying operation totally ineffective.
It has been determined that when powdered filtering and purifying material of the character referring to above is used to filter and purify shortening or oil by establishing a bed of that material atop a screen or paper filter, the bed of material must be maintained rather thin and therefore extended over a substantial or great effective surface area to prevent the bed of material from becoming so dense and compacted as to plug up and prevent a flow of fluid material therethrough. Further, it has been determined that to dependably establish and maintain continuous flow of fluid through such a bed of material, atop a filtering screen, and to prevent the fluid material from causing cavitation in and establishing courses of free flow of fluid through the bed of material, the fluid should be drawn or pulled through the bed of material by a vacuum or minus pressures downstream of the beds and should not be pushed or forced therethrough by positive upstream pressures.
In addition to the above, when shortening or oil is worked upon by vacuum or minus pressures in the course of filtering and purifying it, free oxygen and gases entrained in the shortening or oil is induced and caused to be liberated therefrom, thereby greatly enhancing the effectiveness of the purification process. In the case of working upon the materials with positive or super atmospheric pressures, the reverse is true, that is, entrained free oxygen and gases in the shortening or oil are caused to remain entrained therein to react therewith and accelerate degradation thereof.